In a prime mover-equipped bicycle, when changing a bicycle running over to an engine running, when the crankshaft is driven by artificially operating the pedal to start the engine, the resistance at the time of the compression stroke of the piston will be transmitted to the pedal and, if no sufficient inertia is given to the crankshaft, the engine will be difficult to start and will be required special skill and technique.
Therefore, there has been suggested a decompressing device whereby the pressure in the cylinder is reduced in the initial starting period of the engine so that the crankshaft may be smoothly rotated in the initial period, and when a sufficient rotating inertia is given, the pressure reduction will be stopped so that thereafter a compression may be easily made by the inertia to secure starting of the engine.
When such decompressing device is applied to a prime mover-equipped bicycle, such problems as discussed hereinbelow will be produced in operating the decompressing device.
Because the decompressing operation is made with a lever or the like separately from the engine starting and speed change, it will be necessary to separately perform a decompressing operation at the time of the starting operation, and the operation will be difficult and complicated. It will also be necessary to return the lever properly in time with the starting and special skill and technique will be required for the operation. Such operations are undesirable in instances in which such vehicles, i.e., prime mover-equipped bicycles, are operated by females and children. It is desired that the engine can be positively started while being simply and easily decompressed, even by females and children.